Zealand Pharma's stock fell approximately 20% on the Copenhagen exchange following the release of trial data revealing that 20% of participants discontinued its weight-loss drug due to gastrointestinal side effects. The discontinuation rate represents a significant tolerability concern for the company as it competes in the rapidly growing GLP-1 receptor agonist market alongside established players like Novo Nordisk's semaglutide and Eli Lilly's tirzepatide, both of which have demonstrated stronger safety profiles in clinical trials.

The trial results highlight the competitive intensity in the weight-loss drug space, where tolerability has become a key differentiator for market adoption. Investors will be watching closely for additional data on whether Zealand can address the gastrointestinal side effects through dosing adjustments or formulation changes, and how the company's regulatory pathway and commercialization strategy may be affected by these findings. The margin between accepted side effect profiles and drug discontinuation rates will likely shape Zealand's ability to capture market share against more established competitors.